Knowledge Base

Video Slave

Using multiple video devices

Using multiple video devices

With Video Slave it is possible to playback using multiple video devices at the same time. This article tells you what to look out for to get the best performance for your particular use case.

One important feature that sets Video Slave apart from other solutions on the market is its flexibility when it comes to video output devices.

With Video Slave, you can play out to multiple video output destinations at the same time and Video Slave will do its best to keep all video devices in proper sync with each other and the incoming timecode (if used). For each video device there are separate settings so you can decide what each video device should display in a very fine grained manner (details are explained in this article).

There are currently three different types of video devices available in Video Slave:

Screen video devices (Internal Video Device and Fullscreen Video Device)There are currently two screen video devices in Video Slave. The first is the video player view in the main window. The other one is the fullscreen window.

Blackmagic video devicesVideo Slave supports playout through Blackmagic DeckLink, UltraStudio and Intensity devices. When the application is started, it scans the system for the available devices. PCIe cards or external devices with multiple outputs show up as separate video devices per output. In Video Slave Studio, two Blackmagic devices can be used at the same time

AJA video devicesVideo Slave also supports playout through devices from AJA's KONA, Io and T-TAP product range. As with Blackmagic devices, Video Slave scans the system for available devices when it is launched. PCIe cards or external devices with multiple outputs show up as separate video devices per output. In Video Slave Studio, two AJA devices can be used at the same time.

Performance

For each enabled video device, Video Slave renders video frames several times per second (depending on the settings and the type of device). Thus, it is crucial to only set the devices enabled that you really need. Each render pass uses precious computing time and using more devices than actually needed can cause hiccups during playback.

If you're using two Blackmagic or AJA devices when doing ADR for example, you should consider turning off the internal and fullscreen video devices to avoid hiccups and stutters during playback.

Video Slave and the Avid Video Engine in Pro Tools

If Video Slave is used on the same machine that also runs Pro Tools 11 or later, we recommend that you turn off the Avid video engine. You can do so by opening the Playback Engine window in Pro Tools and uncheck the checkbox labelled "Video Engine". After disabling the video engine, it is important to restart Video Slave if you're using Blackmagic or AJA cards. Pro Tools apparently blocks the video hardware if the Avid video engine is turned on. We also learned that turning off the video engine in Pro Tools positively affects Video Slave's performance.

My device doesn't show up, what can I do to troubleshoot?

If an attached device doesn't show up in the device list, this typically has one of two reasons.

Outdated driverOne reason may be an outdated driver. Video Slave uses the official software development kits (SDKs) offered by Blackmagic Design and AJA respectively to communicate with the devices. Other software applications like e.g. Pro Tools seem to use a different way to communicate with them. Dozens of posts can be found online from audio people complaining about sync drift occurring with newer driver versions where older versions didn't have these issues (or at least the issue was not as severe). From our standpoint, there's no reason to use Video Slave with an older driver version for better performance for example or less sync drift. In our experience, newer drivers have never made things worse (quite the contrary actually).

Another software using the device
If your drivers are up to date, another reason the device won't show up in the preferences can be because another software application is already using the device. This can be an audio application like Pro Tools (see above) or another one you have installed.

Notes on using the fullscreen mode in Video Slave 4

With the release of Video Slave 4 we switched to using Apple's official fullscreen API. This however can cause that all of the attached screens (except for the one Video Slave uses for fullscreen) go black when the fullscreen mode is entered.

To get around this, please open the macOS system preferences -> Mission Control and make sure "Displays have separate spaces" is set.